The invention relates to improvements in hose couplings or similar couplings in general, and more particularly to improvements in couplings of the type wherein one of the tubular components to be sealingly connected to each other is provided with an external retaining part which can be engaged by one or more radially outwardly and inwardly movable arms or claws on a sleeve-like coupling member. Still more particularly, the invention relates to improvements in couplings which are provided with locking elements in the form of rings or like parts capable of being shifted relative to and around the respective sleeve-like coupling members to permit or prevent disengagement of the arms from the external retaining part of the one tubular component. Couplings of the above outlined character are normally provided with O-rings or with other suitable elastic sealing elements which prevent leakage of fluid from the tubular components into the atmosphere or in the opposite direction when the arms engage the external retaining part and the locking element is maintained in a position in which the arms are urged toward the peripheral surface of the adjacent tubular component.
A drawback of certain presently known couplings of the above outlined character is that, when the coupling is used to establish a separable sealing connection between two tubular members (e.g., between a flexible elastic hose and a rigid metallic pipe), unavoidable manufacturing tolerances (even minor tolerances) enable the pipe to become tilted relative to the sleeve-like coupling member and/or the locking element to become tilted relative to the coupling member. This is often compounded by extensive wear upon the parts of the coupling and/or tubular components as a result of repeated engagement and disengagement of the coupling so that the axis of one of the two interconnected tubular components no longer coincides with the axis of the other tubular component. This entails non-uniform stressing of the sealing elements and results in leakage of the confined fluid or in penetration of atmospheric air into the pipeline. The situation is aggravated if the coupling is utilized under the hood of or elsewhere in a motor vehicle, e.g., to establish a path for the flow of fuel, oil or coolant, because the coupling is subject to continuous vibration when the engine is on and/or when the vehicle is in motion. Non-uniform deformation of the sealing element or elements is likely to persist if the sealing elements are cooled in cold climates well below the freezing point. This results in hardening of sealing elements (normally O-rings) and in pronounced leakage of confined fluid when the vehicle is in motion or the engine is on. Leakage of fuel or another fluid in a motor vehicle can have serious consequences.
Another drawback of the just described conventional couplings is their cost. The cost is relatively high because the retaining arms are separately produced parts and the locking element must be biased to its operative position by one or more springs.
In accordance with another prior proposal (reference may be had to German patent application No. 37 41 250 of Rosch published Jun. 15, 1989), the locking element surrounds the arms in such a way that the arms are free to move radially inwardly and outwardly in the internal space of the locking element when the latter is maintained in the inoperative position. When the locking element is shifted to the operative position, an internal surface of such element prevents radially outward movements of the arms so that the arms are compelled to remain in engagement with an external rib on one of the tubular components, e.g., on a metallic pipe which is to be sealingly coupled to a flexible hose. The internal surface of the locking element has a frustoconical shape and is dimensioned to force the arms toward the pipe as soon as the locking element assumes its operative position. The external surface of the tubular coupling member is provided with alternating annular ribs and grooves cooperating with complementary annular grooves and ribs of the locking element to maintain the latter in a selected axial position. The cooperating ribs and grooves are intended locking element from its operative or inoperative position. A drawback of such proposal is that the operator must exert a pronounced force in order to move the locking element axially of the tubular sleeve-like coupling member. Moreover, the operative position of the locking element relative to the coupling member must be changed at certain intervals in order to compensate for wear upon such parts and/or to compensate for manufacturing tolerances. The coupling of Rosch comprises a substantial number of separately produced parts which contributes to the initial cost. Certain parts are to be secured to each other by form-locking connections, or the parts must be secured to each other by glue, which also contributes to the initial cost. Moreover, the establishment of a reliable form-locking connection, or of a connection which relies on adhesive, necessitates the making of parts to be secured to each other with a rather high degree of accuracy. All this is necessary in order to prevent wobbling of the coupled-together tubular components because such wobbling can affect the sealing action of the O-rings and can entail the development of paths for the leakage of fluid between the interior of the tubular components and the surrounding atmosphere.
German patent application No. 1 912 316 of Stephany (published Sep. 20, 1970) discloses a coupling for the establishment of a leakproof connection between a hose and a pipe which is provided with an external retaining rib. The coupling comprises a tubular coupling member which carries radially movable axially extending elastic arms serving to engage an external rib of the pipe. A ring-shaped locking element surrounds the coupling member and is movable axially of the coupling member between operative and inoperative positions. The arms can move apart to be disengaged from the external rib of the pipe when the locking element is moved to the inoperative position. The locking element has rigid straight internal ribs which bear upon the arms in the operative position of the locking element to prevent disengagement of the arms from the rib at the exterior of the pipe. The internal ribs surround the respective arms with a certain amount of clearance because the locking element must remain free to turn relative to the tubular coupling member. It has been found that extensive wear upon the parts of the coupling which is disclosed by Stephany, in addition to manufacturing tolerances, results in the establishment of paths for leakage of confined fluid after a relatively short period of use. More specifically, the pipe is free to wobble relative to the coupling member and to thus affect the action of one or more O-rings which are installed between the pipe and the coupling member.